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Comment—A New Angle on Strophomenid Paleoecology: Trace-Fossil Evidence of an Escape Response for the Plectambonitoid Brachiopod Sowerbyella rugosa from a Tempestite in the Upper Ordovician Kope Formation (Edenian) of Northern Kentucky (Dattilo, 2004)

¹ Department of Geological Sciences & Allison Center for Marine Research, San Diego State University, San Diego, CA, 92182–1020; leighton@geology.sdsu.edu

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In his recent article, Dattilo (2004) suggested that strophomenide brachiopods, in particular the plectambonitoid Sowerbyella, were capable of active locomotion, and even burrowing. The article argues that Sowerbyella was capable of living quasi-infaunally and upright, with the shell edgewise—a position that could be obtained by burrowing.

As Dattilo summarizes, the consensus view (Rudwick, 1970; Richards, 1972; Alexander, 1975; Alexander and Scharpf, 1990; Leighton and Savarese, 1996; Leighton, 1998) of strophomenide life-position is that relatively immobile strophomenides lived convex-valve down. Dattilo notes that the primary argument of these studies was based on functional tests and conclusions, but that these studies assumed that the free-lying strophomenides were incapable of extensive movement. Dattilo, however, points out that if this assumption of relative immobility is incorrect, then strophomenides would be capable of achieving any orientation. As such, hypotheses that concavo-convex brachiopods lived with the convex-valve up (Lescinsky, 1995) would be plausible, and Dattilo argued that the epibiont-distribution data presented by Lescinsky, supporting a convex-valve up orientation, has not been refuted. Dattilo further suggests that Lescinsky's data were dismissed (Leighton, 1998) on the grounds of functional considerations (i.e., strophomenide immobility) that are not necessarily valid.

This brings up an important point about the nature of functional evidence. Functional morphology has a poor reputation because many functional studies have been relatively sparse in data; functional hypotheses were often analogous to Kiplingesque "just-so" stories (Gould and Lewontin, 1979). It is interesting that the convex-up versus convex-down debate seemed to be indicative of a more modern approach to functional morphology in paleontology. For the past 35 years there has been a series of studies using two primary approaches for addressing orientation questions in the fossil record: epibiont distribution and biomechanical experiments. Both approaches aim . . . [Full Text of this Article]